The present invention relates to a sample measuring method and a charged particle beam apparatus and more specifically to a charged particle beam apparatus that does not contaminate the sample.
A process assessment is performed by measuring a pattern width as by a CD-SEM (Critical Dimension-Scanning Electron Microscope) after resist application, exposure and development. More specifically, to check by a scanning electron microscope represented by CD-SEM whether a pattern formed on a sample such as semiconductor wafer is properly formed, a sample is moved by a sample stage so that an electron beam can be radiated against a desired pattern.
In such an apparatus, if a contaminant is adhering to a surface of the sample, scanning an electron beam over a portion where the contaminant is present means that the electron beam scans the surface of the contaminant, making it impossible to produce a true sample image or obtain correct measurements of sample dimensions. A technique to solve this problem is disclosed in Patent Document 1.
JP-A-11-329328 proposes that, before introducing a sample into a sample chamber in an electron beam inspection apparatus, the sample is heated by a heater installed in a preliminary exhaust chamber of the electron beam inspection apparatus to remove the contaminant. It is also described in JP-A-5-135752 that, when the sample examination is not performed, an organic gas produced from grease used in the sample stage is removed by heating it to 50-60° C.
It has been found in recent years that contaminants may adhere to semiconductor wafers as they undergo measurement or inspection by a scanning electron microscope. If these contaminants adhere to a semiconductor wafer, air bubbles may be formed in a resist during a subsequent resist application process. Because of the air bubbles, the resist may be formed thin, which in turn will likely to result in another problem that pits may be formed in a base material during a dry etch process.
Investigations by the authors of this invention have found that contaminants adhering to the sample are fluorocompounds used as a lubricant in the electron microscope. The fluorocompounds can mostly be removed if subjected to a cleaning process. However, to shorten the time taken by the semiconductor manufacturing process as much as possible, it is desired that the sample be transferred directly to the resist application process following the measurement or inspection by the scanning electron microscope, without undergoing the cleaning process.
The technique disclosed in JP-A-11-329328 performs heating of the sample before introducing the sample into the sample chamber. This can temporarily remove the contaminants. However, contaminants that adhere to the sample in the sample chamber remain on the sample, giving rise to a problem that the contaminants can cause failures in the subsequent manufacturing process.
Further, as disclosed in JP-A-5-135752, it is conceivable to heat the sample chamber. Since materials that are weak to heat, such as O-ring, are used in some cases in the sample chamber, heating the sample chamber itself is not preferred. Vaporized grease may adhere to inner walls of the sample chamber, from which it may fly to the sample.